Ir(III) Metal Emitters with Cyano‐Modified Imidazo[4,5‐b]pyridin‐2‐ylidene Chelates for Deep‐Blue Organic Light‐Emitting Diodes

Abstract Ir(III) carbene complexes have been explored as one of the best blue phosphors for their high performance. Herein, the authors designed and synthesized a series of blue‐emitting Ir(III) phosphors (f‐ct9a–c), featuring fac‐coordinated cyano‐imidazo[4,5‐b]pyridin‐2‐ylidene cyclometalates. These Ir(III) complexes exhibit true‐blue emission with a peak maximum spanning 448–467 nm, with high photoluminescence quantum yields of 81–88% recorded in degassed toluene. Moreover, OLED devices bearing phosphors f‐ct9a and f‐ct9b deliver maximum external quantum efficiencies (EQEmax) of 25.9% and 30.3%, together with Commission Internationale de L'Eclairage (CIE x,y ) coordinates of (0.157, 0.225) and (0.142, 0.169), respectively. Remarkably, the f‐ct9b‐based device displays an incredible EQE of 29.0% at 5000 cd·m−2. The hyper‐OLED device based on f‐ct9b and ν‐DABNA exhibits an EQEmax of 34.7% and CIEx,y coordinates of (0.122, 0.131), affirming high potentials in achieving efficient blue electroluminescence.

General information and materials.All reactions were conducted under N 2 atmosphere.
Commercially available reagents were used without further purification and solvents were dried prior to use. 1 H and 19 F NMR spectra were measured with Bruker Avance III 400 MHz NMR instrument.Mass spectra were recorded on a Dionex 2D-LC (Bruker micrOTOF-Q LC/MS/MS) liquid chromatograph-mass spectrometer system.TGA measurements were performed on a TA Instrument TGAQ50, at a heating rate of 10 C min −1 under a nitrogen atmosphere.
Photophysical measurements: UV-Vis spectra were recorded on a HITACHI UH-4150 spectrophotometer.The steady-state emission spectra were measured with Edinburgh FS 980.Both wavelength-dependent excitation and emission responses of the fluorimeter were calibrated.The lifetime studies were performed by a time-correlated single photon counting system (TCSPC).
Spectral grade solvents (Merck) were used as received.To determine the photoluminescence quantum yield in solution, samples were degassed using at least three freeze-pump-thaw cycles.
The solution quantum yields are calculated using the standard sample which has a known quantum yield.
Electrochemistry: Cyclic voltammetry was conducted on a CHI621A Electrochemical Analyzer.
Ag/Ag + (0.01 M AgNO 3 ) electrode was employed as reference electrode.The oxidation and reduction potentials were measured using a glassy carbon working electrode with 0.1 M of NBu 4 PF 6 in CH 3 CN, respectively.The potentials were referenced externally to the ferrocenium/ferrocene (Fc + /Fc) couple.

Computational details of theoretical investigations:
The geometries, electronic structures, and electronic excitations of the studied Ir(III) complexes were investigated at the B3LYP-D3(BJ)/def2-SVP level [1] with Gaussian 16 set of programs. [2]The solvent effect of toluene was taken account by the polarizable continuum model (PCM). [3]The corresponding ground state (S 0 ) and lowest triplet state (T 1 ) geometries were optimized based on the X-ray structural data of f-ct9a -c.A total of 10 low-lying excited states (T 1  T 5 and S 1  S 5 ) were included in the TD-DFT calculation [4] based on the optimized S 0 structure.Natural transition orbital (NTO) analysis was applied to obtain a clear and compact orbital representation for the electronic excitation described by a variety of orbital transitions without a single predominant one (e.g., S 0 →T 1 excitation in this work) at optimized S 0 structure. [5]The IFCT (interfragmentary charge transfer) method analysis in the S 0 → T 1 excitation is using Multiwfn software. [6]The Hirshfeld method is used to calculate the density in IFCT analysis. [7]e spin-orbit coupling (SOC)-TDDFT calculation [8] was performed using B3LYP functional with ZORA Hamiltonian [9] (SARC-ZORA-SVP for Ir and ZORA-def2-SVP for other elements) at the optimized S 0 and T 1 structures in ORCA (v5.0.3) software. [10]A total of 100 low-lying excited states (50 for singlet and 50 for triplet) were included in the SOC-TDDFT calculation in toluene with COSMO model. [11]The radiative lifetime (τ rad ) and radiative rate (k r ) are calculated by the arithmetic average and Boltzmann average (at 298 K) of the three SOC substates of T 1 excited states. [8]vice fabrication and characterization：OLEDs were fabricated on the ITO-coated glass substrates with multiple organic layers sandwiched between the transparent bottom indium-tin-oxide (ITO) anode and the top metal cathode using a Trovato 450C system.Before device fabrication, the ITO glass substrates were pre-cleaned carefully.All material layers were deposited by vacuum evaporation in a vacuum chamber with a base pressure of 10 -4 Pa.The deposition rate of organic layers was kept at 1-2 Å/s.The doping was conducted by co-evaporation from separate evaporation sources with different evaporation rates.The current density, voltage, luminance, external quantum efficiency, electroluminescent spectra and other characteristics were measured with a Keithley 2400 sourcemeter.The EQE measurement system is Hamamatsu C9920-12, which is equipped with Hamamatsu PMA-12 Photonic multichannel analyzer C10027-02 whose longest detection wavelength is 1100 nm.All measurements were repeated three times, among which the median value was chosen as the reported data, and the corresponding errors are generally within ±5%.
Preparation of cyano substituted carbene chelate.

Figure S8 .
Figure S8.Emission spectra of f-ct9a and b with specified co-host and doping concentration at RT.

Figure S9 .
Figure S9.The structure of Device II, energy diagram and chemical structures of the materials used in the devices.

Figure S11 .
Figure S11.Relative luminance as a function of operational time of OLED Device I using (a) f-ct9a and (b) f-ct9b as emitter with L 0 = 1000 cd•m −2 .

Table S2 .
Electroluminescence Data of devices (Device II)